1. Field of the Invention
The present invention relates to an interface device for connecting a control unit and a field apparatus such as sensor and actuator in a network which are, for example, used in a production line, and an interface system using the same.
2. Conventional Art
A conventional electric line connection to the field apparatus such as a sensor and an actuator which are used in a production line was generally constituted through an individual wiring.
Although, these days, such connection is being shifting toward a field network which permits a flexible system construction, however, in such instance an interface device for connecting to a network is necessitated.
Now, an interface necessitates a power source, and in a case of a system where many numbers of field apparatuses are connected to a network having a long laying distance via an interface, the electric power is usually supplied from the network to the interface.
In order to receive such electric power supply, the interface is required to include a regulator unit which converts the voltage supplied from the network into a voltage usable in the interface system, a transceiver for performing signal transmission and reception with the network, a controller unit such as microcomputer which controls a communication system and the field apparatus and an isolator which electrically isolates the network from the field apparatus.
Now, when the scale of the system enlarges, at an interface device located remote from the power source, a voltage drop due to the network increases and the interface device likely becomes inoperable, for this reason structure of the network is limited and the advantages of the field network can not fully make use of, therefore, it is necessary to reduce power consumption of such interface device.
In a conventional interface device a photo coupler is generally used as the isolator, however, the power consumption of such photo coupler is comparatively large and the size reduction thereof is difficult, because the photo coupler is a dedicated part for respective ICs.
For countermeasuring the above problem, for example, JP-A-11-317445 (1999) and JP-A-11-136293 (1999) disclose a semiconductor device of on-chip structure in which a dielectric isolation (DI) substrate such as a silicon on insulator (SOI) substrate is used as a circuit substrate and a static capacitor type isolator is mounted thereon.
By means of the above prior art, the electrical isolation is obtained by the static capacitor not using the photo coupler, therefore, if the interface device is constituted with such means, both small sizing and low power consumption can be easily achieved.
However, the above conventional art did not take into account the noise propagation by the dielectric isolation substrate which causes problems of erroneous operation of the circuits and deterioration of the elements.
When an interface device which is formed by integrating a transceiver unit and a capacitive type isolator unit on an SOI substrate is operated through power supply from the network, the interface device possibly operates erroneously due to noises from the network.
Namely, if noises come into the transceiver unit from the network, a voltage is induced even on a thin film semiconductor layer via a semiconductor support substrate and an erroneous operation due to noises is resultantly caused.
Further, in such instance, performance of the elements on the thin film semiconductor layer is possibly deteriorated due to the noises, which is caused by such as electric charge accumulation in a buried insulation film and occurrence of charge depletion.
Now, the influences of the noises in the conventional art will be further explained in detail with reference to FIG. 3, in a semiconductor device using a dielectric isolation substrate a buried insulation film 41 is formed within a semiconductor substrate as shown in the drawing, thereby, the semiconductor substrate is divided into two parts in its thickness direction, in that an isolated structure is formed one (the lower side in the drawing) as a semiconductor support substrate region 411 and the other (the upper side in the drawing) as a semiconductor region used for circuit element formation.
Further, the semiconductor region used for circuit element formation is further divided in its face direction by a region insulation portion ( insulation channel) 410 into two kinds of thin film silicon layers of a controller side region 407 and a network side region 408.
Namely, in this instance, one piece of semiconductor substrate is divided into three kinds of regions by the region insulation portion 410 and the buried insulation film 412.
Herein, circuits formed in the controller side region 407 is electrically isolated from circuit formed in the network side region 408 and a necessary signal transmission passage is provided by an isolator portion via a static capacitor coupling.
The circuits in the network side region 408 are supplied by a power source V+ and Vxe2x88x92 in the network and the circuits in the controller side region 407 are supplied by a power source VDD2 and GND2 in the controller side.
On the other hand, the semiconductor support substrate region 411 is connected nowhere and is kept floating. Herein, the power source V+ and Vxe2x88x92 in the network is, for example, 24V and if a high voltage noise is induced in the network, the high voltage noise is applied to the network side region 408. The noise voltage at such instance sometimes reaches up to, for example, 500V.
Such noise is directly and electrostatically applied to the controller side region 407 from the network side region 408 via the region insulation portion 410 as well as since the semiconductor support substrate region 411 is kept floating, after inducing a noise voltage at the semiconductor support substrate region 411 via the buried film 412, the noise voltage is applied to the controller side region via the buried insulation film 412 in a voltage divided manner by a static capacitor.
At this moment, since the static capacitance formed by the region insulation portion 410 between the controller side region 407 and the network side region 408 shows merely a small value because of the thin thickness of respective regions 407 and 408, the noises directly applied via this portion does not cause a substantial problem.
On the other hand, since the semiconductor support substrate 410 adjoins with the controller side region 407 and the network side regions 408 through a single plane, a static capacitance formed between them is comparatively large and a noise voltage induced at the controller side region 407 from the network side region 408 via the buried insulation film 412 reaches comparatively high voltage.
At this moment, since the buried insulation film 412 accumulates charges and is depleted, the performance of the elements is deteriorated.
An object of the present invention is to provide an interface device using a dielectric isolation substrate which sufficiently suppresses an erroneous operation due to noises and performance deterioration, and a system using the same.
The above object is achieved by an interface device which is provided with at least two semiconductor regions separated from a support substrate region via a dielectric body and in which an electrical isolation between an integrated circuit formed in the respective semiconductor regions is provided by a static capacitance, and is further provided with means for keeping the potential of one of the semiconductor regions, in which the integrated circuits being connected to a network are formed, at a potential of a power source line for the network.
At this instance, the integrated circuits being connected to the side of the network can include a communication function for an integrated circuit in another interface device connected to the network.
Further, at this instance, the interface device can include a package and the support substrate region can be connected to a pin in the package via an electrode and a lead frame or alternatively the support substrate region can be connected to a power source electrode in the integrated circuits being connected to the side of the network.
Likely, the above object is achieved by an interface device which is provided with at least two semiconductor regions separated from a support substrate region via a dielectric body and in which an electrical isolation between integrated circuits formed in the respective semiconductor regions is provided by a static capacitance, and further in which the integrated circuits being connected to the side of the network are provided with a first device having a first break down voltage characteristic and a second device having a second break down voltage characteristic lower than the first break down voltage characteristic and the first device is supplied from a first power source and the second device is supplied from a second power source which is insulated from the first power source.
Further, the above object can be achieved by an interface system which is constituted by a plurality of above any interface devices connected via a common network.
Now, the problem of the above conventional art will be explained, in that because a potential difference between the thin film silicon layer and the semiconductor support substrate is caused and the element formed in the thin film silicon layer is affected by an electric field caused by the potential difference, the characteristic of the elements vary, accordingly, the problem can be resolved by a condition in which no potential difference is caused between the semiconductor support substrate and the thin film silicon layer.
Further, the interface device for the network is operated by being connected to the network. Namely, the power source potential of the circuits formed in the thin film layer being connected to the network varies in response to the power source potential variation in the network.
Accordingly, in order to prevent from causing a potential difference between the semiconductor support substrate and the thin film silicon layer connected to the network, if the semiconductor support substrate is connected to the network so that the potential of the semiconductor support substrate assumes the same potential of the network, the problem can be resolved.
As has been explained in connection with FIG. 3 prior art, the region forming the circuit elements are separated into the two regions of the network side region 408 and the controller side region 407 by the region insulation portion 410. Namely, the power source for the circuits formed in the network side region 408 is supplied from the network power source V+ and Vxe2x88x92, and the controller side region 407 is electrically insulated from the network side region 408.
Therefore, if the semiconductor support substrate 411 is connected to the network, the network side region 408 and the semiconductor support substrate 411 are kept at the same potential as the network power source, therefore, even if a common noise is induced at the network power source line, no potential difference due to the noise is caused between the network side region 408 and the semiconductor support substrate 411.
Accordingly, with the above measure the influence of noises to the elements formed in the network side region 408 can be prevented.
On the other hand, the controller side region 407 is connected to the controller side power source VDD2 and GND2, and is electrically insulated from the network side region 408.
Accordingly, as in the above measure, when the semiconductor support substrate 411 is connected to the network, since the semiconductor support substrate 411 is connected to the network power source, if a common noise is induced at the network power source line, a potential difference due to the noise induced at the network power source line is caused between the controller side region 407 and the semiconductor support substrate 411, therefore, the elements formed in the controller side region 407 are possibly affected by the noise in the network.
Now, the elements formed on the SOI substrate include a kind of elements which is greatly affected by the network noise and another kind of elements which is little affected by the network noise.
For example, a MOS transistor having a high break down voltage is the former kind of elements which is likely affected by the noise and a usual MOS transistor which operates below 5V is the latter kind of elements which is hardly affected by the noise.
Since, the noise from the network affects the element from the side of the semiconductor support substrate, the elements of the kind of which element region is formed to extend near the region of the semiconductor support substrate side is likely affected by the noise, and on the contrary the elements of the kind of which region is formed thin on the surface of the semiconductor is hardly affected by the noise, because the elements are separated distantly from the semiconductor support substrate side.
Therefore, if the elements of the kind which are hardly affected by the noise are formed in the controller side region 407 and the elements of any kinds are formed in the network side region 408, the influence of the noise induced at the network power source line can be eliminated.